Tube drawing pen



NOV. 10, 1970 w. DAHLE 3,5392%9 TUBE DRAWING PEN Filed May 15. 1969 [Il /ill;

J" INVENTOR:

A TTO/QNEV United States Patent C US. Cl. 401-259 7 Claims ABSTRACT OF THE DISCLOSURE A tube drawing pen in which the drawing tip is screwed into a sleeve to which an ink chamber may be tightly attached. The corresponding external and internal screw threads on the drawing tip and in the sleeve are considerably narrower than the flutes between the threads so that, when the drawing tip is screwed into the sleeve until its rear end abuts against a conical inner stop surface in the sleeve, the flanks of the threads tightly engage at one side with each other, while the remaining open part of the flutes form a long spinal ventilating channel.

The present invention relates to a tube drawing pen which comprises a drawing tip which is screwed into a holder and the peripheral surface of which is provided with a ventilating channel.

Due to their advantageous features, these so-called tube drawing pens are being used more and more frequently as drawing tools by artists and draftsmen. Such a tube drawing pen consists of a drawing tip which is inserted into a holder of any desired shape or into an intermediate element. The peripheral surface of such a drawing tip is usually provided with a ventilating channel which is preferably spirally curved or consists of longitudinal and transverse grooves and extends along the length of the part of the drawing tip, which is removably secured to the holder or intermediate element by being screwed or plugged into it.

All of these tube drawing pens have in common that it is diflicult to secure the drawing tip in the holder or intermediate element in a manner so as to prevent the ink from leaking out of the joint between the tip and the holder. This is due to the fact that changes in pressure occur in the ink chamber because of variations in air pressure or an increase in temperature. These pressure differences are to 'be compensated by the ventilating channels.

The manner of securing the drawing tip to the inside of the holder or intermediate element by means of screw threads has the disadvantage that the ink which ascends and descends within the ventilating channel which traverses the threads also penetrates by capillary action through the threads and thereby soils the pen on the outside. This danger of penetration of ink by capillary action even occurs in tube drawing pens of the type in which the drawing tip is plugged into the holder or the intermediate element since it is very difficult to engage the associated surfaces so tightly with each other that not even a very small gap will occur between them.

For these reasons it is necessary to treat such drawing tools rather delicately and to clean them very carefully and frequently. This necessarily entails a waste of time and requires the draftsman often to interrupt his work to clean his pen and possibly his hands as well which might also have become soiled by the leaking pen. Such leaking due to the mentioned capillary action may also cause the place of work of the draftsman as well as his other drawing tools to be soiled and may even ruin his Work completely. In order to overcome these disadvantages, the present applicant has made numerous experi- 3,539,269. Patented Nov. 10, 1970 ments with compensating channels and compensating tubes, but these experiments were also unsuccessful for the same reasons as previously stated, namely, because of the disadvantages of the usual screw or plug connections.

It is an object of the present invention to provide a tube drawing pen of the type as first described above, which, even though its ventilating means is at all times very effective, completely avoids any leaking of ink due to capillary action from the joint between the drawing tip and its holder or the intermediate element into which the drawing tip is inserted. According to the invention, this object is attained by securing the drawing tip by a screw connection to the inner side of the holder or the intermediate element and by making the associated threads themselves, that is, those projecting inwardly from the drawing tip and those projecting outwardly from the holder or intermediate element, of a width smaller than the width of the flutes between the threads. When the drawing tip is screwed tightly into the holder or intermediate element, the flanks of the projecting threads of the two elements will then be pressed tightly at one side against each other.

According to the invention, the screw threads and their flutes have two functions, namely, to secure the drawing tip within the holder or the intermediate element While the Wider flutes between the threads form a spirally shaped ventilating channel. By employing the flutes of the threads as a ventilating channel, this channel has the best possible length insuring an effective pressure balance between the ink chamber and the outer atmosphere.

Another feature of the invention provides that, when the drawing tip is screwed into the holder or the intermediate element, its inner end abuts against a stop which is preferably provided in the form of an inner conical surface in the holder or the like upon which the inner end of the drawing tip engages so as to form a tightly sealed joint. Thus when the drawing tip is screwed to a sufficient depth into the holder or intermediate element, the flanks of the screw threads will be pressed tightly against each other and in addition the rear open end of the drawing tip will also be tightly closed.

Another feature of the invention provides that the associated screw threads have a trapezoidal or rectangular cross section so that when they are screwed tightly together a substantially flat surface contact will be formed between the adjacent flanks which insures that these flanks will be in a tightly sealing engagement with each other and capillary effects will be avoided. Such threads have the further advantage that their fian ks may be very accurately made by very simple means.

The invention further provides that the clearance which according to the invention is provided between the screw threads and the flutes between them has a non-capillary cross-sectional size in the axial and radial directions. Consequently, no capillary effects can also occur on the draw ing tip and the holder or intermediate element between the crests of the threads and the base of the flutes.

The features and advantages of the present invention will become further apparent from the following detailed description thereof which is to be read with reference to the accompanying drawings, in which:

FIG. 1 shows an enlarged central longitudinal section of a tube drawing pen according to the invention, while FIG. 2 shows an elevation of the tip unit of the drawing.

As illustrated in the drawing the rear part of the tip unit 1 of the drawing pen according to the invention facing the ink chamber 2 has a hollow cylindrical part 3 of a relative large inner diameter the conical front end 5 of which is tapered in the direction toward the ink outlet opening or nip 4 of the pen. This inner cone 5 terminates into a bore 6 in which the thin drawing tube 7 is mounted. The hollow cylindrical part 3 contains a weight mem her 8 which is axially slidable therein with considerable play and carries on its front end a very thin wire 9 which is adapted to keep the ink passage unclogged which extends through the drawing tube 7.

The hollow cylindrical part 3 of the tip unit 1 is provided with an external thread, generally indicated by the nu meral 10, by means of which the tip unit 1 is screwed into an internal thread, generally indicated by the numeral 11 in a sleeve 12. The associated projecting threads 13 and 14 on sleeve 12 and on the part 3 are narrower than the flutes 15 and 16 between these threads. The flat crests 17 and 18 of threads 13 and 14 are spaced at a noncapillary radial distance from the base of the flutes 15 and 16 into which they engage. The external thread 10 and the internal thread 11 may be of a trapezoidal cross section, although they may also be of a rectangular or square cross section.

The cross-sectional dimensions and the length of the ventilating or compensating channel which remains free between the threads 13 and 14 are made so as to be in a very particular relation to the cross section of the ink channel and to the contents of the ink chamber 2.

When the tip unit 1 is screwed into the sleeve 12, its rear end 19 engages upon an inner cone 20 which is integral with the sleeve 12. Into the open rear end of the hollow cylindrical part 3 of the tip unit 1 a cylindrical tube 21 is screwed which serves as a stop for limiting the distance of the axial movement of the weight member 8 without, however, preventing the free flow of ink from the ink chamber 2. This tube 21 serves in addition as a guide to facilitate the insertion of the rear end 19 of the tip unit 1 into the inner cone 20.

The front end of the ink chamber 2. is plugged tightly into an annular groove in the rear end of sleeve 12 so as to be sealed tightly to the latter. The ink passes from the ink chamber 2 through the tube 21 and then through a transverse bore 23 in the cylindrical part 3 into the ventilating channel which remains between the flanks of the threads 13 and 14.

When the tip unit 1 is screwed into the sleeve 12 until its rear end engages tightly upon the inner cone 20, this engagement prevents the tip unit 1 from being screwed more deeply into the sleeve 12. If the tip unit 1 is further turned in the same direction the flanks of the threads 13 and 14 will be pressed tightly against each other in the direction toward the ink outlet opening 4.

If at the inside of the drawing pen a certain overpressure relative to the outer atmosphere is produced, for example, due to heating of the pen by the hand of the draftsman, the ink will pass from the ink chamber through the small bore 23 for a certain distance into the spiral ventilating channel which is formed between the flutes 1'5 and 16 of the threads. Thus, there 'will be no underpressure at the inside of the pen but a pressure which holds the ink column in the spiral ventilating chamber 15, 16 in balance. If the draftsman now draws with his pen and ink is withdrawn from the ink container 2, an underpressure will be formed at the inside of the pen since the ventilating chamber is partly filled with ink and no air can therefore pass through it from the outside. This underpressure at first causes the ink to be drawn back from the ventilating channel and thereafter draws so much air through this free channel until the pressure at the inside of the pen is again balanced with the atmospheric pressure at the outside of the pen. Ink can therefore penetrate into the ventilating channel 15, 16 only if the pressure at the inside of the pen increases beyond the outside pressure. As long as this does not occur, the ventilating channel remains open. Only when the inside pressure increases beyond the outside pressure, ink will again be forced into a part of the ventilating channel and will again be sucked out of it when an underpressure is formed in the pen due to the flow of ink through the ink channel when the draftsman is drawing. Thus, a regular pumping action occurs in the pen. If an underpressure occurs at the inside of the pen, this underpressure sucks the ink out of the ventilating channel and thereby opens the channel to the outside which, in turn, eliminates the underpressure. As long as the ventilating chamber contains no ink, the inside of the pen and the outer atmosphere can freely communicate with each other.

Although my invention has been illustrated and described with reference to the preferred embodiments thereof, Iwish to have it understood that it is in no way limited to the details of such embodiments but is capable of numerous modifications within the scope of the appended claims.

Having thus fully disclosed my invention, what I claim 1. In a tube drawing pen comprising a tip member having a tubular rear part with an open rear end and an external thread on a considerable part of the length of said tubular part, a thin drawing tube secured in and projecting from the front end of said tip member and communicating with the inside of said tubular part, a weight member slidable in the axial direction in said tubular part and having a very thin wire secured to its front end and extending axially through and slidable along said drawing tube a sleeve member having an internal thread corresponding to and having substantially the same length as said external thread, and an ink chamber removably but tightly connected to the rear end of said sleeve member, each of said threads having flanks and spiral flutes between said flanks of said threads, said flanks on one side of said threads adapted to engage tightly with each other when said tubular part is screwed as far as possible into said sleeve member, each of said threads having a considerably smaller Width than said spiral flutes so that when said tubular part is screwed into said sleeve member, the parts of said flutes between said flanks form a relatively long spiral ventilating channel, and a shorter channel connecting the rear end of said ventilating channel 'with said ink chamber.

2. A tube drawing pen as defined in claim 1, further comprising a stop member, said tubular part when screwed into said sleeve member engaging upon said stop memher.

3. A tube drawing pen as defined in claim 2, in which said stop member forms an integral part of said sleeve member.

4. A tube drawing pen as defined in claim 3, in which said stop member is formed by an inner conical surface in said sleeve member, the rear end of said tubular part engaging into and being in a tight sealing engagement with said conical surface when said tip member is screwed tightly into said sleeve member.

5. A tube drawing pen as defined in claim 1, in which said threads have a corresponding substantially trapezoidal cross section and one of the flan-ks of one of said threads is adapted to engage with a surface contact with the opposite flank of the other thread.

6. A tube drawing pen as defined in claim 1, in which said threads have a corresponding substantially rectangular cross section and one of the flanks of one of said threads is adapted to engage with a surface contact with the opposite flank of the other thread.

7. A tube drawing pen as defined in claim 1, in which the crests of said threads are radially spaced from the bottoms of said flutes so that a non-capillary clearance is formed between them.

References Cited UNITED STATES PATENTS 3,466,132 9/1969 Riepe 401259 FOREIGN PATENTS 831,656 2/ 1952 Germany.

15,430 11/1905 Great Britain.

LAWRENCE CHARLES, Primary Examiner 

